He may have won the election, but now President Obama faces enormous challenges in the House and Senate – among Republicans and Democrats. To succeed, he must do what does not come naturally to him: Spend lots of quality time with lawmakers of both parties.

President Obama speaks at his election night party in Chicago in the wee hours of Nov. 7. On the president's immediate agenda: how to avoid the fiscal cliff. Op-ed contributor John J. Pitney Jr. writes: 'Much of the mass media interpreted the election as a defeat for the GOP. The House Republicans see it differently.'

Claremont, Calif. — Now that President Obama has won his campaign against Mitt Romney, he has to start another on Capitol Hill. On issues ranging from the impending fiscal cliff to implementation of health-care reform, he needs support from Congress, especially GOP House Speaker John Boehner. The president will have to work very hard to get that support, because his victory in the first campaign does not guarantee success in the second.

Each party in each chamber confronts him with a different challenge.

Much of the mass media interpreted the election as a defeat for the GOP. The House Republicans see it differently. At the start of the campaign, Democrats were hoping that Medicare would be their weapon to take down the GOP majority. They tried to tie Republican lawmakers to Paul Ryan’s premium-support proposal, claiming that it would end Medicare as we know it. Republicans countered the assault by accusing their foes of trying to raid Medicare to pay for the president’s health-care law. They fought the issue at least to a draw, and kept control of the House by a comfortable margin.

This outcome may embolden Republicans to keep pressing for change in Medicare and other social welfare programs. As Winston Churchill wrote, “Nothing in life is so exhilarating as to be shot at without result.”

House Democrats may be glad that Mr. Obama won, but they owe him very little. The president’s unpopularity in Republican-leaning states hurt Democratic congressional candidates, especially in the South. The president also failed to give House Democrats as much attention and campaign help as they wanted.

When a Wall Street Journal reporter asked Obama campaign manager Jim Messina why the president wasn’t doing more for congressional candidates, he said: "We really do believe a high tide raises all boats. If we win, history teaches us Democrats will win, as well." But while the president floated, the House Democrats’ boat remained stuck on bottom.

Senate Democrats fared better than their House counterparts, not only holding their majority but scoring a net gain of two seats. Yet the president cannot take much credit for this showing. Their biggest upset triumphs occurred in Montana and North Dakota, which went for Mitt Romney in the presidential race. They also won high-profile races in the Romney states of Missouri and Indiana. These victories were less surprising because the Republican candidates had made spectacular blunders while talking about rape and abortion. The president may have had coattails in a couple of other races, but Democrats would have held their majority without them.

Disappointed about their 2012 setbacks, Senate Republicans will be counting the days until the 2014 midterm, which will give them another chance to gain a majority. Of the 33 seats up that year, Democrats currently hold 20, so they have much more to lose. Moreover, seven of these Democrats come from Romney states, whereas only one of the 13 Republicans (Susan Collins of Maine) represents a state that President Obama just won. Senate Republicans will feel relatively little election-year pressure to side with the White House.

So what can the president do? One important part of his legislative strategy should be to look for issues of common ground. Speaker Boehner has already signaled that House Republicans are willing to deal on tax reform. In theory, this issue should appeal across partisan and ideological boundaries. Liberals and Democrats like the idea of closing loopholes that benefit the rich. Conservatives and Republicans want to lower marginal rates. And people across the spectrum would be glad if a simplified system cut paperwork and saved billions in compliance costs.

The key words here are “in theory.” In practice, every tax preference has a constituency and every scrap of tax paperwork has a rationale. During the mid-1980s, President Reagan overcame these obstacles and persuaded Congress to pass an important tax-reform bill. It might be hard to replicate that success in 2013. Congress is more polarized, and the opponents of tax reform are savvier – in part because they learned from their defeat at Reagan’s hands.

Even if President Obama comes up with a smart legislative strategy, he will still have to change his operating style. During his first term, the cerebral chief executive often stayed aloof from the personal politicking that had enabled other presidents to get their way on Capitol Hill. As one Democratic lawmaker told Politico earlier this year, “I’ve been on Air Force One twice – with George W. Bush.”

To succeed, the president must do what does not come naturally to him: Spend lots of quality time with lawmakers of both parties, paying attention to their personal interests and policy ideas.

Congratulations, Mr. President, you’ve made it through a hard year. Unfortunately, you have another one coming up.